PBr 6 or PBr 7 are Earth Colors, they exist in any shade of yellow, orange, red or violet brown to green brown.

The RCW has the quantity of colors making the color wheel, a color number from 3RCW, 6, 12, 24, 36 etc. The tint to shade numbers from .09 to .9 and the warm to cool value numbers from .1 to .9. Each pigment color has it's own three diget number distinguishing it from any other color.

Opposite color, Thalo Blue Transparent.

To make a dark neutral with Cadmium Red light Opaque
mix it with the opposite color Thalo Blue.

Being a secondary color opposite Thalo Blue it is useful in making a very dark neutral often happening in the evening.

These words are colored in a tint of Cyan, see how nicely opposites complement each other? Cyan is called Phthalo Blue or Thalo Blue, depending on the brand. Both words come from the chemical word Phthalocyanine. The color's descriptive name is Transparent Cyan. I use the color Cadmium Red Light for my standard palette.

Cadmium Red Light is not as dark as Cadmium Red Medium. It is easier to make Cadmium Red Medium or Deep by adding transparent Magenta PR:122. Use opaque orange make a Red-Orange. Opaque yellow would make a muddy, chalky color. I found I use the color Red Light more than Red Medium or Deep.